1. Field of the Invention
The instant disclosure relates to a power transistor; in particular, to a trenched power metal-oxide-semiconductor field-effect transistor (MOSFET).
2. Description of Related Art
To reduce the gate/drain capacitance and to increase the breakdown voltage without increasing the on-resistance, prior art power MOSFETs include shielding electrodes at lower portions of gate trenches.
However, normally, during the process of manufacturing trenched power MOSFET with shielding electrode structure, the dielectric layer on the side wall at the upper portion of the gate trench is etched away in advance and then the new gate dielectric layer is deposited, and during the process of etching away the dielectric layer, the depth of etching is difficult to control. An etching that goes too deep will cause holes or slits formed on the gate trench.
The holes or slits are likely to affect the electrical properties of the trenched power MOSFETs. If a voltage is applied to the gate of a MOSFET with holes or slits on its gate trench, these holes and slits may cause leakage currents between the gate and the source such that the MOSFET has poor electrical properties.